In pharmaceutical delivery systems, it is sometimes necessary to mix a drug in powder form with a diluent in order to be able to deliver the drug to a subject. This can be done manually by injecting the diluent into a vial containing the powdered drug, mixing the drug into the diluent and aspirating the drug in fluid form into a syringe for subsequent injection into the subject. Such manual procedures are generally considered to be cumbersome and inconvenient and often lead to wastage of some of the drug as it may remain in the vial.
Also known in the art are dual chambered syringes which use a by-pass channel to provide fluid communication between the two chambers. The two chambers are commonly defined within a syringe barrel by two separate pistons and an end stopper spaced apart within the syringe barrel. In such an arrangement, the two chambers are placed in fluid communication by the by-pass channel by actuation of the outer most piston within the syringe barrel. This causes both pistons within the syringe barrel to advance to a point where the inner most piston becomes aligned with the by-pass channel. At that point, further actuation of the outer most piston causes fluid contained in the chamber between the two pistons to flow into the outwardly extending by-pass channel and around the inner most piston which remains stationary.
With the two chamber syringe barrel and external by-pass arrangement described above, a danger exists in the possibility that the inner most piston is pushed too far along such that it goes past the by-pass channel before full transfer of the diluent occurs. This may be caused by an overly vigorous application of the plunger to the outer most piston. Once the inner most piston is pushed past the by-pass channel without having allowed proper fluid flow from the first chamber to the second chamber, it can be extremely difficult to correct.
With some pharmaceutical constituents, in order to properly constitute the pharmaceutical substance, it is desirable to ensure that the mixing of the two constituents occurs slowly and evenly.